1. Field of Invention
The present invention relates to a system and a method for controlling NOx. More particularly, the present invention relates to a system and a method for controlling NOx that can predict NOx amount generated in an engine of a vehicle without an additional NOx sensor and can control NOx by using the predicted NOx amount.
2. Description of Related Art
As emission regulations for vehicles having an internal combustion engine becomes stricter and stricter, it is required for reducing emission during operation of the internal combustion engine. One method for reducing emission is to reduce emission generated in each cylinder of the internal combustion engine during combustion of an air/fuel mixture.
Another method for reducing emission is to use a post-processing system of an exhaust gas in the internal combustion engine. The post-processing system of the exhaust gas is adapted to convert noxious materials generated at each cylinder during combustion of the air/fuel mixture into harmless materials. For this purpose, catalytic converters are used for converting carbon monoxide, hydrocarbon, and nitrogen oxide into harmless material.
In order to efficiently convert noxious materials by using the catalytic converters of the exhaust gas, technique for controlling the NOx is necessary. In order to control the NOx, it is necessary to precisely predict the NOx amount generated in the engine.
According to conventional arts, devices for analyzing the exhaust gas or sensors for detecting the NOx amount are used so as to predict the NOx amount precisely. If the devices for analyzing the exhaust gas or the sensors for detecting the NOx amount, cost may increase. In addition, compositions in the engine exhaust gas may contaminate the devices for analyzing the exhaust gas or the sensors for detecting the NOx amount and the sensors themselves are out of order.
In order to solve above-mentioned problems, technique for predicting NOx amount is developed. Reliability, however, may be deteriorated according to the technique due to very complicated calculation processes and very simplified assumptions for simplifying the calculation processes.
Since it is hard to obtain precise and reliable NOx amount according to the technique, a method for controlling the NOx based on the predicted NOx amount cannot be relied on.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.